Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751411AbdIRV3N (ORCPT ); Mon, 18 Sep 2017 17:29:13 -0400 Received: from mail-io0-f170.google.com ([209.85.223.170]:47353 "EHLO mail-io0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750783AbdIRV3M (ORCPT ); Mon, 18 Sep 2017 17:29:12 -0400 X-Google-Smtp-Source: AOwi7QAbHbsH54T7AKJl64mgpncV2+3U+RdN8wEHupc5KkvvD3draXCxB+cncOEY/ZEIjEXR4zNJ4Q== Date: Mon, 18 Sep 2017 15:29:09 -0600 From: Tycho Andersen To: Mark Rutland Cc: linux-kernel@vger.kernel.org, Marco Benatto , kernel-hardening@lists.openwall.com, linux-mm@kvack.org, Juerg Haefliger , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v6 07/11] arm64/mm, xpfo: temporarily map dcache regions Message-ID: <20170918212909.3x7i7pmh76a4l24s@docker> References: <20170907173609.22696-1-tycho@docker.com> <20170907173609.22696-8-tycho@docker.com> <20170914182555.GB1711@remoulade> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170914182555.GB1711@remoulade> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2055 Lines: 58 On Thu, Sep 14, 2017 at 07:25:56PM +0100, Mark Rutland wrote: > On Thu, Sep 07, 2017 at 11:36:05AM -0600, Tycho Andersen wrote: > > From: Juerg Haefliger > > > > If the page is unmapped by XPFO, a data cache flush results in a fatal > > page fault, so let's temporarily map the region, flush the cache, and then > > unmap it. > > > > v6: actually flush in the face of xpfo, and temporarily map the underlying > > memory so it can be flushed correctly > > > > CC: linux-arm-kernel@lists.infradead.org > > Signed-off-by: Juerg Haefliger > > Signed-off-by: Tycho Andersen > > --- > > arch/arm64/mm/flush.c | 7 +++++++ > > 1 file changed, 7 insertions(+) > > > > diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c > > index 21a8d828cbf4..e335e3fd4fca 100644 > > --- a/arch/arm64/mm/flush.c > > +++ b/arch/arm64/mm/flush.c > > @@ -20,6 +20,7 @@ > > #include > > #include > > #include > > +#include > > > > #include > > #include > > @@ -28,9 +29,15 @@ > > void sync_icache_aliases(void *kaddr, unsigned long len) > > { > > unsigned long addr = (unsigned long)kaddr; > > + unsigned long num_pages = XPFO_NUM_PAGES(addr, len); > > + void *mapping[num_pages]; > > > > if (icache_is_aliasing()) { > > + xpfo_temp_map(kaddr, len, mapping, > > + sizeof(mapping[0]) * num_pages); > > __clean_dcache_area_pou(kaddr, len); > > + xpfo_temp_unmap(kaddr, len, mapping, > > + sizeof(mapping[0]) * num_pages); > > Does this create the mapping in-place? > > Can we not just kmap_atomic() an alias? Or is there a problem with that? I think what we really want is something like vmap(), looking at xpfo_temp_map() it seems like the implementation is completely wrong. I wonder if what you mentioned at LSS is possible though: doing cache management with userspace primitives instead of mapping the region just to flush it. Cheers, Tycho